Various kinds of scanning probe microscopes such as AFM (Atomic Force Microscope), MFM (Magnetic Force Microscope), and SNOM (Scanning Near-Field Optical Microscope) are all of the type of microscope which uses a special microscopic probe to detect certain types of interaction between the probe and the surface of a sample, for instance, tunneling current, atomic force, magnetic force, and scanning near-field electro-magnetic wave. Then, using a piezo-electric ceramic scanner having displacements in three axes, allows the probe to scan the surface of the sample in front-and-back as well as left-and-right directions. It also utilizes the capability of minute adjustment in the vertical axis and feedback circuit to maintain its location. The interaction between the probe and the sample during the scanning process makes the distance, which is anywhere between several .ANG. (angstroms) to several hundred .ANG., relatively constant. One can obtain the interactive action chart of the sample's surface so long as one records the minute-adjusted distance in the vertical axis for each point on the scanned surface. This data can be used to derive the surface characteristic of the sample.
The strain probe microscope of the prior art is used to measure the minute action of the microscopic probe by using the reflex refracted angle of a laser. By using a laser to focus on the probe, the beam reflects back to the laser sensor to measure the deformation on the probe by taking the signal measured from the laser sensor. In order to obtain the optimum amplified signal, one uses the increase of the reflection distance to project and amplify the strain signal of the probe, hence the range of required space is relatively large. Also, this type of probe system needs a lot of elements including: the probe, a laser diode, a reflex mirror focusing object lens, a splitted laser inductor, and a signal processing circuit; which have the shortcomings of being complicated in structure, expensive in terms of optical elements and not easily used.
Although the disclosure of U.S. Pat. No. 5,386,720 to Toda appears to be similar to that of the present invention, however, the objective is completely different. The major difference is that the wire terminals 220, 18, 129, 222, 312, 314, 316 as shown in the Figures and discussed in the specification in the Toda patent are located at the bottom of the cantilever while those of the present invention are on the top of the cantilever. The major disadvantage of placing wire terminals at the bottom is that it is hard to connect wires to them, for example element 44 in FIG. 2, since the height of the probe tip is very small (several .mu.m). The diameter and the connection of the wire 44 will affect the scanning action of the probe tip and the test piece. The present invention in contrast changes the location of the wire terminal to the top of the cantilever. Besides, the Toda patent discloses fabrication only of the main body of the cantilever and the respective processing circuit is an exterior type as shown in FIG. 2, FIG. 12, FIG. 16, and FIG. 17, but the volume and space it occupies are all relatively large which will result in the situation that the volume of the overall probe microscope can not be reduced. Besides this disadvantage, since the exterior processing circuits (236, 238, 240) need wire connections, these wire connections will cause the signal interference and noise which will further reduce the signal accuracy. Also, the length of the piezoresistive material becomes longer than what it normally is because of the relatively long wire which will result in high noise and a relatively low signal-to-noise ratio. In order to resolve the space and noise problems, the present invention fabricates the circuit at the terminal of the cantilever which can handle the signal nearby and also reduce the volume, thereby, increasing the signal-to-noise ratio and further raising the overall measuring accuracy and ability of the probe.
U.S. Pat. No. 5,266,801 makes use of the piezoelectric or piezoresistive materials to measure the strain on the cantilever, but it still has the noise problem left irresolvable for the signal along the connecting wire. Also, the exterior transfer and processing circuit occupies a relatively large space and complicates the system structure.
U.S. Pat. No. 5,400,647 measures, by using an Atomic Force Microscope, the transverse force which is related to the magnitude of the frictional force. The Atomic Force Microscope makes use of the optical way to measure the deformation of the cantilever. Similar to other prior art Atomic Force Microscopes, since they have many optical elements, their system spaces are relatively large, their structures are relatively complicated, and the noise problems of their connecting wires still exist.
U.S. Pat. No. 5,468,959 is a method for measuring the surface not the particular elements of the probe apparatus itself. Although the patent does mention the probe in FIG. 5, however, this probe is not the focus of the patent. This patent mainly describes the use of capacitor and electro-static force, and the measurement of displacements and external electro-static force. This kind of probe is relatively hard to fabricate and its characteristic is still under evaluation.